/*
 * SIP Communicator, the OpenSource Java VoIP and Instant Messaging client.
 *
 * Distributable under LGPL license.
 * See terms of license at gnu.org.
 */
package net.java.sip.communicator.impl.neomedia.codec.audio.silk;

/**
 * Second order ARMA filter 
 * Can handle slowly varying filter coefficients
 *
 * @author Jing Dai
 */
public class Silk_biquad 
{
    /**
     * Second order ARMA filter
     * Can handle slowly varying filter coefficients
     * @param in input signal
     * @param in_offset offset of valid data.
     * @param B MA coefficients, Q13 [3]
     * @param A AR coefficients, Q13 [2]
     * @param S state vector [2]
     * @param out output signal
     * @param out_offset offset of valid data.
     * @param len signal length
     */
	static void SKP_Silk_biquad(
		    short      []in,        /* I:    input signal               */
		    int          in_offset,
		    short      []B,         /* I:    MA coefficients, Q13 [3]   */
		    short      []A,         /* I:    AR coefficients, Q13 [2]   */
		    int        []S,         /* I/O:  state vector [2]           */
		    short      []out,       /* O:    output signal              */
		    int          out_offset,
		    final int    len         /* I:    signal length              */
		)
	{
	    int   k, in16;
	    int A0_neg, A1_neg, S0, S1, out32, tmp32;

	    S0 = S[ 0 ];
	    S1 = S[ 1 ];
	    A0_neg = -A[ 0 ];
	    A1_neg = -A[ 1 ];
	    for( k = 0; k < len; k++ ) {
	        /* S[ 0 ], S[ 1 ]: Q13 */
	        in16  = in[ in_offset + k ];
	        out32 = Silk_macros.SKP_SMLABB( S0, in16, B[ 0 ] );

	        S0 = Silk_macros.SKP_SMLABB( S1, in16, B[ 1 ] );
	        S0 += ( Silk_macros.SKP_SMULWB( out32, A0_neg ) << 3 );
	        

	        S1 = ( Silk_macros.SKP_SMULWB( out32, A1_neg ) << 3 );
	        S1 = Silk_macros.SKP_SMLABB( S1, in16, B[ 2 ] );
	        tmp32    = Silk_SigProc_FIX.SKP_RSHIFT_ROUND( out32, 13 ) + 1;
	        out[ out_offset + k ] = (short)Silk_SigProc_FIX.SKP_SAT16( tmp32 );
	    }
	    S[ 0 ] = S0;
	    S[ 1 ] = S1;
	}
}
